Human milk provides antibodies and non-antibody factors that may account for breast feeding protecting from symptomatic shigellosis. Virulence mechanisms of Shigella spp are shared with other enteropathogens. This proposal addresses the relationship between shared mechanisms of virulence and human milk factors that interact with these shared factors. We hypothesize that human milk factors which protect against Shigella spp. also provides protection against other enteropathogens that express related virulence proteins. The specific aims address both sigA and non IgA protective factors. Aim 1. Define the role of anti-invasion plasmid antigen [anti-IPA] antibodies in protection from shigellosis by determining the relationship between quantity of milk antibodies to baculovirus expressed recombinant IpaB, IpaC and IpaD in human milk and symptom status of breast-fed infants who become infected with Shigella spp. Aim 2. Define the role of cross protective anti-Ipa sigA by characterizing human milk antibodies directed toward invasion plasmid antigen epitopes shared by Shigella spp., invasive E. coli (EIEC) and Salmonella spp. Aim 3. Define the role of human milk antibodies to shigatoxin produced by S. dysenteriae serotype 1 by characterizing the ability of isolated affinity purified anti-B subunit sIgA derived from human milk to block toxin-induced HeLa cell cytotoxicity and accumulation of hemorrhagic fluid in rabbit ileal loops. Aim 4. Determine the role of non-antibody milk factors (anti-inflammatory [cytokine binding] factors, lactoferrin, shigatoxin-binding glycolipids) which interact with Shigella spp. virulence factors in tissue culture (HeLa cell invasion) and animal models (rabbit enteritis and rabbit ligated ileal loop) of pathogenesis.